You can increase your power storage in Last Fortress by doing the following:
- Upgrading Power Generator
- Building and upgrading Capacitor Rooms
- Upgrading McKinley’s second skill “Expansion”
Upgrading the generator will increase the power capacity as follows:

And so on…
You can build up to five Capacitor Rooms. Each one will require a certain level of Power Generator to be unlocked. So if you don’t have them available, just keep upgrading the Generator.

McKinley’s second skill “Expansion” grants a +% to your current power capacity. Hence, it won’t be very effective early on when your capacity is low.

Next Question: Is it worth buying N.A.T.E.?